1. Field of the Invention
This invention relates generally to mailing systems and more particularly to an interface between a system processor and a plurality of peripheral devices.
2. Further Related Applications
The present invention includes an interface board which interconnects a postage value determining system processor with a plurality of peripheral devices associated with a mailing system. In U.S. Pat. No. 4,308,579, issued to Daniel F. Dlugos entitled Multiprocessor Parcel Postage Metering System Having Serial Data Bus, and assigned to the assignee of the present invention, a postage calculation system having a serial communications controller for communications between the system processsor and peripheral devices was disclosed.
The system included a serial communication bus through which the peripheral devices associated with the mailing system communicated with the system processor. Some peripherals were interconnected to the serial communications bus by a peripheral controller, while a meter setting device was directly linked to the serial communications bus. Appropriate signals were transmitted along a bus attention line when it was desired to have a particular peripheral device receive or transmit via the communications bus. Acknowledgment lines were provided for acknowledging receipt of signals. The communications controller comprised an integral part of the main postage calculator system circuit board.
Since the serial controller was an integral part of the main system circuit board, a purchaser who only wished to acquire a postage scale and not the peripheral devices or not all of the available peripherals was at a cost disadvantage in terms of the serial controller and the memory occupied for peripheral communications formatting programs. In addition, if a malfunction arose, the serial communications controller and the communications bus were not serviceable as a single unit on a separate board.
The sharing of a common communications bus by all peripheral devices made the replacement or substitution of different peripheral devices a formidable task which required reprogramming of the main circuit board for both data and command formatting, as well as protocol and communications routines.